This invention relates to techniques and systems for controlling the temperature of fluids. More particularly, this invention relates to devices for controlling the temperature of fluids used with internal combustion engines.
Thermal control of engine lubricating oil and other fluid temperatures can provide significant advantages. For example, it is generally helpful to preheat engine oil prior to startup to reduce engine wear during this period. Preheated engine oil can also reduce high emission levels that are generally produced at startup due to low initial engine operating temperatures.
In addition, under steady state conditions, it is desirable to limit lubricating oil temperatures as resulting lower peak engine temperatures are known to enhance the longevity of the oil and the various engine components. Lower peak oil temperature permits oil to perform its lubricating function more effectively.
Automotive engines are now generally required-to run hotter than in the past in order to meet the goals of improved fuel economy and lower emissions. With the incorporation of an oil cooler, oil temperatures can be reduced. This permits the lubricating oil and resulting engine operating temperature to be run at a lower, more optimal temperature level. In some cases for certain large vehicles, such as class 7-8 trucks, part of the water cooling system is used for oil cooling. However, these cooling systems can add significant weight, cost, and complexity to the vehicle.
Particularly for larger vehicles such as trucks, it is advantageous to maintain a lower, more consistent oil temperature because this allows the oil to better carry soot to the oil filter. Achieving improved oil stability permits the use of lighter weight oils, which are known to generally result in improved fuel economy.
Furthermore, when higher levels of exhaust gas recirculation (EGR) are introduced back into the engine for further combustion in order to reduce harmful emissions and increase gas mileage, the resulting oil temperature is estimated to increase approximately 20xc2x0 F. EGR is also known to introduce more soot into oil, thus decreasing oil life by exacerbating oil breakdown. Oil breakdown allows soot to aggregate, producing larger particles which can lead to oil filtration problems. Thus, improved thermal management systems are needed for engine fluids, such as engine oil.
The present invention provides carbon foam based thermal regulators, systems and methods thereof. In a preferred embodiment, the thermal regulator is adapted to provide both heating and heat exchanging. The heating feature is helpful at engine startup, while the heat exchange feature can be used to reduce engine oil and overall engine operating temperatures.
A temperature regulator includes at least one carbon foam element, the foam element for electrically heating fluids. Two locations on the carbon foam element are adapted for receiving electrical connectors thereto. The carbon foam element can provide an electrical resistivity of between 1 to 500 xcexcohmxc2x7meter at 25xc2x0 C. The carbon foam element can be used to heat liquids, such as oil, ethylene glycol, brake fluid, transmission fluid and power steering fluid.
In a preferred embominent, at least a portion of the carbon foam is thermally and electrically conductive. In this embodiment, the carbon foam element can be thermally connected to an active cooling device. The active cooling device can be a heat exchanger having a shell side and a tube side, wherein the shell side comprises the thermally conductive carbon foam element. The carbon foam element can comprise graphite foam and provide a thermal conductivity of at least 50 W/mxc2x7K.
The electrically conductive carbon foam element may be disposed in an oil container, and may include a flanged portion. A thermostat can be included for triggering heating of the carbon foam element when the temperature is below a predetermined minimum temperature and for terminating the heating when the temperature is at or above a predetermined maximum temperature.
In another embodiment, a combustion engine includes an engine block and at least one carbon foam element, the foam element extending into the engine block or disposed in thermal contact with at least one engine fluid. When the carbon foam element is disposed in the engine block, the carbon foam element can include at least two locations each adapted for receiving electrical connectors thereto. The carbon foam element can be used to provide passive cooling or active cooling. In the active cooling embodiment, the carbon foam element is thermally connected to the active cooling device, such as a heat exchanger having a shell side and a tube side, wherein the shell side comprises a graphite foam element, the graphite foam has a thermal conductivity of at least 50 W/mxc2x7K.
A method for controlling the temperature of fluids includes the steps of providing at least one electrically conductive carbon foam element, the electrically conductive foam element being thermally connected to a fluid, and heating the fluid by dissipating electrical current across the electrically conductive foam element. The heating can be initiated when the fluid is at a temperature below a first predetermined temperature, and terminate when the fluid is at a temperature above a predetermined maximum temperature. The method can also include the step of cooling the fluid after the fluid reaches a predetermined cooling temperature.
The fluid can include other states of matter associated therewith, such as particulates and semi-solid matter, such as states that can be present during injection molding or the pulling of fibers. The method can also include the step of controlling the viscosity of fluids.
A temperature regulation system includes a temperature regulator including at least one electrically conductive carbon foam element, the electrically conductive foam element for electrically heating fluids, and a structure for applying a potential difference across the electrically conductive carbon foam element. The electrically conductive carbon foam element can be adapted to heat fluids, such as oil, ethylene glycol, brake fluid, transmission fluid and power steering fluid. The electrically conductive carbon foam element can also provide cooling to fluids.
A method for operating a combustion engine includes the steps of providing at least one electrically conductive carbon foam element, the foam element thermally connected to an engine fluid, and at least one of heating the engine by dissipating electrical current across the electrically conductive carbon foam element when the engine is at a temperature below a predetermined minimum operating temperature and cooling the engine if the engine temperature is at or above a maximum operating temperature. The cooling comprises radiating heat through a thermally conductive carbon foam element. The heating can be terminated when the fluid heating step results in the temperature being above a predetermined shutoff temperature.
The thermally conductive carbon foam element can be graphite foam and can extend into the engine block. The graphite foam can provide a thermal conductivity of at least 50 W/mxc2x7K.
A heat spreader includes at least one thermally conductive carbon foam element, the carbon foam element adapted to be placed in thermal contact with a region to be cooled. The foam element draws heat from the region to be cooled and distributes the heat across its volume. The region for cooling can be included in a medical application, food process equipment or an engine.